Connected: An Internet Encyclopedia
RFC 1812 - 5.3.5.2 Directed Broadcasts

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### 5.3.5.2 Directed Broadcasts

A router MUST classify as network-prefix-directed broadcasts all valid, directed broadcasts destined for a remote network or an attached nonsubnetted network. Note that in view of CIDR, such appear to be host addresses within the network prefix; we preclude inspection of the host part of such network prefixes. Given a route and no overriding policy, then, a router MUST forward network- prefix-directed broadcasts. Network-Prefix-Directed broadcasts MAY be sent.

A router MAY have an option to disable receiving network-prefix- directed broadcasts on an interface and MUST have an option to disable forwarding network-prefix-directed broadcasts. These options MUST default to permit receiving and forwarding network-prefix- directed broadcasts.

DISCUSSION

  There has been some debate about forwarding or not forwarding directed broadcasts. In this memo we have made the forwarding decision depend on the router's knowledge of the destination network prefix. Routers cannot determine that a message is unicast or directed broadcast apart from this knowledge. The decision to forward or not forward the message is by definition only possible in the last hop router.

Next: 5.3.5.3 All-subnets-directed Broadcasts

Connected: An Internet Encyclopedia
RFC 1812 - 5.3.5.2 Directed Broadcasts